Base bias circuit, and power amplifier using the base bias circuit

ABSTRACT

A base bias circuit ( 1 ) operates like a constant voltage source, and a base bias voltage generated thereby varies according to fluctuation of the environment temperature without being influenced by the supply voltage, to hold a collector bias voltage constant. The base bias circuit ( 1 ) has a function of controlling the base bias voltage according to a control signal coming from the outside. By using a resistor ( 6 ) and resistor ( 14 ) having suitable resistances, the bipolar transistors constituting the bias circuit ( 1 ) can be small in size to reduce the electric current consumed by the bias circuit ( 1 ) thereby to make unnecessary the RF choke inductor between a power transistor ( 13 ) and the bias circuit ( 1 ). In short, the cost is lowered by making the chip size small and by reducing the number of external parts.

FIELD OF THE INVENTION

[0001] This invention relates to a base bias circuit for use in a poweramplifier and the power amplifier.

BACKGROUND OF THE INVENTION

[0002] A base bias circuit operating like a constant voltage source isindispensable for a power amplifier using a common-emitter bipolartransistor. The constant voltage source is more suitable than a constantcurrent source as the bias circuit from the following reasons.

[0003] It is assumed that a RF input is applied to the common-emitterbipolar transistor given a bias to a base under the constant voltagesource. In case where input RF power is sufficiently low, thecommon-emitter bipolar transistor operates with a low signal. Therefore,a collector current is equal to a collector bias current flowing in asuch state that no signal is given to the amplifier.

[0004] On the contrary, as the input RF power is increased, thecollector current of the common-emitter bipolar transistor is increasedso as to reach several times or higher of the collector bias current.Due to the increase of the collector current, a higher saturation outputand lower distortion can be realized.

[0005] In the meantime, in the case where the bias is given to the baseunder the constant current source, the collector current is constantlykept to hFE times of the base bias current, so that the collectorcurrent is not increased even if the input RF power is increased.

[0006] Accordingly, when the collector bias current is set in the samemanner that the base bias is given under the constant voltage source, again compression upon a high-signal operation occurs under a lower inputRF power. This degrades saturation characteristic, reduces additionalpower efficiency and deteriorates linearity.

[0007] Further, when the collector bias current is equal to thecollector current under such a case that the base bias is given underthe constant voltage source and the input RF power is high, a highcollector current flows even when no RF signal is given or the input RFpower is low. Therefore, consumption power is problematically increased.

[0008] From the aforementioned reasons, the base bias circuit operatinglike the constant voltage source is indispensable for the poweramplifier using the common-emitter bipolar transistor. Specifically, anoutput resistance in a direct current state of the base bias circuit maybe equal to or lower than a base input resistance in the direct currentstate of the common-emitter bipolar transistor of the amplifier.

[0009] For the base bias circuit, the following facts will be required.

[0010] At first, the bias voltage given to the base must be strictlyspecified because the common-emitter bipolar transistor has an extremelyhigh mutual conductance gm.

[0011] Therefore, it is necessary that the base bias circuit has such astructure that a generated base bias voltage is not affected byfluctuation of a power supply voltage.

[0012] Moreover, the collector current of the common-emitter bipolartransistor is exponential function of temperature. Therefore, the basebias circuit must be constituted so that the generated base bias voltageis varied in dependence upon fluctuation of environment temperature tokeep the collector bias current constant.

[0013] In a CDMA system portable phone, a transmission power must becontrolled. In the base bias circuit, it is therefore required that thegenerated base bias voltage is functionally variable in accordance witha control signal from the external in order to reduce the consumptionpower of a power amplifier under a low transmission power.

[0014]FIG. 2 shows an example of a conventional base bias circuit.

[0015] A base bias circuit 52 is composed of an npn type bipolartransistors 53, 54, 55 and a resistor 56. All of the bipolar transistors54, 55, 53 and 58 are manufactured by the same semiconductor process,and a ratio of emitter areas is set 1:n:1:n. A collector of the bipolartransistor 58 is directly connected to an RF load in a high-frequencystate while it is directly connected to a power supply in a DC state.

[0016] Initially, consideration will be made of such a case that the RFinput power is not given. In the circuit illustrated in FIG. 2, aportion consisting of the bipolar transistors 54, 55 and another portionconsisting of the bipolar transistors 53, 58 are symmetricallyconstituted in the DC state except that the collector of the bipolartransistor 55 is connected to the base of the bipolar transistor 54while the collector of the bipolar transistor 58 is directly connectedto the power supply in the DC state.

[0017] Herein, if the voltage VCE between the emitter and the collectoris 0.3-0.5 or higher, the portion consisting of the bipolar transistors54, 55 and the portion consisting of the bipolar transistors 53, 58 areconsidered to be symmetrically and completely constituted in the DCstate because the collector current of the bipolar transistor is notalmost dependent upon VCE in general. Specifically, an emitter arearatio of the bipolar transistors 54, 55 and an emitter area ration ofthe bipolar transistors 53, 58 are 1:n, respectively.

[0018] Further, the base potential of the bipolar transistor 54 is keptequal to the base potential of the bipolar transistor 53. From theabove-mentioned facts, the base-emitter voltage VBE of the bipolartransistor 55 is substantially equal to VBE of the bipolar transistor58, and VBE of the bipolar transistor 54 is substantially equal to VBEof the bipolar transistor 53.

[0019] Therefore, the collector currents flowing along the bipolartransistors 55 and 58 are equal to each other while the collectorcurrents flowing along the bipolar transistors 54 and 53 are also equalto each other. In this event, the bipolar transistor 53 placed in anoutput portion of the base bias circuit 52 forms an emitter follower.Taking this into consideration, it is found out that the output voltageof the bias circuit 52 is kept to a value lower with VBE than the basepotential of the bipolar transistor 53. In other words, the base biascircuit operates like the constant voltage source.

[0020] In case where this fact is analyzed in more detail, the outputresistance of the bias circuit 52, namely, the direct current resistanceviewed the side of the bias circuit 52 from the emitter of the bipolartransistor 53 is substantially equal to a direct current base resistanceof the power transistor 58.

[0021] In this event, it is assumed that hFE of the bipolar transistoris sufficiently high, and the base current of the bipolar transistor 54and the base current of the bipolar transistor 53 are negligibly low forthe collector current of the bipolar transistor 55.

[0022] The base potential of the bipolar transistor 54 is substantiallyequal to 2×VBE. In the case where a voltage given to a control terminalis set to Vref and a resistance value of the resistor 56 is set to R,the current flowing along the resistor 56 is given by (Vref-2×VBE)/R.This becomes the collector current of the bipolar transistor 55 inalmost such a state.

[0023] As described above, the collector currents flowing along thebipolar transistors 55 and 58 are equal to each other. Taking this intoconsideration, the collector current of the bipolar transistor 58 isalso equal to (Vref-2×VBE)/R. Therefore, it is found out that thecollector current is not affected by the power source voltage.

[0024] Herein, VBE of the bipolar transistor is generally almostconstant irrespective of the collector current. Taking this intoaccount, it is confirmed that the collector current of the bipolartransistor 58 is controlled as linear function.

[0025] In this event, the bias voltage given to the base of the bipolartransistor is directly controlled. Taking this into consideration, thecollector bias current becomes the exponential function, and therefore,slight fluctuation of the base bias voltage causes large fluctuation ofthe collector bias current.

[0026] In contrast, the collector bias current becomes the linearfunction of the control voltage in the base bias circuit 52, andtherefore, the fluctuation of the collector bias current for thefluctuation of the control voltage is suppressed to a sufficiently lowvalue.

[0027] Further, when the environment temperature is varied, thecharacteristic of each bipolar transistor is also varied. As mentionedabove, in the circuit illustrated in FIG. 2, the portion consisting ofthe bipolar transistors 54, 55 and the portion consisting of the bipolartransistors 53 and the power transistor 58 are symmetricallyconstituted. To this end, the affect of the characteristic fluctuationof the bipolar transistor 54 and the affect of the characteristicfluctuation of the bipolar transistor 53 are canceled to each otherwhile the affects of the characteristic fluctuations of the bipolartransistor 55 and the power transistor 58 are canceled to each other. Asa result, such a structure is not readily subjected to the affect of theenvironment temperature.

[0028] However, the conventional technique illustrated in FIG. 2 hasseveral problems.

[0029] As a first problem, the emitter area of the bipolar transistor 55must be equal to the emitter size of the power transistor 58. Even ifthe power transistor, for example, has an output of about 1 W for use inthe portable phone, a chip size is extremely large.

[0030] Therefore, the bias circuit comprising the bipolar transistor 58having the same emitter as the power transistor 58 has the chip sizelarger than the power transistor 58.

[0031] As a second problem, the collector current flowing along thebipolar transistor 55 is equal to the collector bias current flowingalong the power transistor 58. This means that the consumption currentof the bias supply circuit 52 is substantially equal to the consumptioncurrent of the power transistor 58.

[0032] As a third problem, a choke inductor 62 is necessary between thebias supply circuit 52 and the power transistor 58 in order to preventthe RF signal from leaking to the bias circuit.

[0033] The output portion of the bias circuit 52 is structured by theemitter follower consisting of the bipolar transistor 53. Herein, thebase potential of the bipolar transistor 53 is constantly kept to about2×VBE by an operation of a circuit block . Taking this into account, itis found out that the output impedance of the emitter followerconsisting of the bipolar transistor 53 is relatively low underhigh-frequency.

[0034] Accordingly, in order to prevent the input RF signal to the powertransistor 58 from leaking to the side of the bias circuit, the chokeinductor 62 is required. In the case where an exterior part is used asthe choke inductor 62, a mounting cost and a cost for the exterior partis additionally necessary. In case where an inductor device formed on asemiconductor substrate is used as the choke inductor 62, the chip areais increased.

[0035] As the conventional technique for solving the first problem andthe second problem, the ratio of the emitter areas of the bipolartransistors 54, 55, 53, 58 is set to 1:n:m:m×n in the bias circuitillustrated in FIG. 2.

[0036] In this case, the emitter area ratio of the bipolar transistors54 and 55 is set to 1:n, the emitter area ratio of the bipolartransistors 53 and 58 is also set to 1:n, and the circuit blockconsisting of the bipolar transistors 54, 55 and the circuit blockconsisting of the bipolar transistors 53, 58 keeps symmetricalcharacteristic.

[0037] Therefore, functions required for the base bias circuit can berealized. Namely, the bias voltage given to the base is not affected bythe fluctuation of the power supply voltage, the base bias voltage isvaried in dependence upon the fluctuation of the environment temperatureso as to keep the collector bias current constant, and the generatedbase bias voltage is variable in accordance with the control signal fromthe external.

[0038] Further, the collector current flowing along the bipolartransistor 55 becomes low with 1/m times of the collector currentflowing along the power transistor 58, and therefore, the reduction ofthe consumption power can be realized. Moreover, the emitter area of thetransistor having the largest emitter size becomes low with 1/m times,and therefore, the circuit area is reduced in accordance with a methodof selecting m.

[0039] However, such a third problem that the choke inductor isnecessary is not solved. Although the circuit area becomes lowest in thecase of m=n, two transistor each having the emitter area of n isrequired, and there is a predetermined limit for reducing the area ofthe bias circuit.

[0040] Moreover, although the consumption current of the bias circuitbecomes lowest in the case of n=1, the bipolar transistor having thesame emitter area as the power transistor is necessary in the biascircuit, so that the circuit area is not reduced.

[0041] Thus, the conventional circuit has the limit for reducing theconsumption current and area. Further, the choke inductor for preventingthe leak of the RF power is indispensable between the base bias circuitand the power transistor, the exterior part and the additional mountingcost is necessary, or an on-chip inductor having a large area isrequired.

[0042] It is therefore an object of this invention to provide a basebias supply circuit which has a small chip area and a low consumptioncurrent without a choke inductor between a base of a power transistorand a bias supply circuit and which is for use in a bipolar transistor,and an amplifier circuit using the same.

DISCLOSURE OF THIS INVENTION

[0043] A base bias circuit according to this invention supplies a biascurrent to a base of a common-emitter bipolar transistor of an npn typefor a power amplifier.

[0044] The base bias circuit comprises first through third bipolartransistors of an npn type and first and second resistors integrated ona semiconductor substrate and a base bias current control terminal.

[0045] The first resistor is inserted between the base bias currentcontrol terminal and the first bipolar transistor.

[0046] The second resistor is inserted between a base of the secondbipolar transistor and the first bipolar transistor.

[0047] A base of the second bipolar transistor is connected to acollector of the third bipolar transistor.

[0048] An emitter of the second bipolar transistor is connected to abase of the third bipolar transistor.

[0049] An emitter of the third bipolar transistor is grounded. Acollector of the first bipolar transistor is connected to a positivepower supply. An emitter of the first bipolar transistor is directlyconnected to the base of the bipolar transistor for the power amplifier.

[0050] In this event, a third resistor may be inserted between aconnection point of the first and second resistor and a base of thefirst bipolar transistor, and the emitter of the third bipolartransistor may be grounded via a fourth resistor.

[0051] Further, it may be short-circuited by the use of a metal wiringinstead of the second resistor.

[0052] In addition, the first and second bipolar transistors may bereplaced by n-type MOSFETs, and a buffer circuit may be inserted betweenthe first resistor and the base bias current control terminal.

[0053] For example, the buffer circuit comprises a fourth bipolartransistor of an npn type and fifth and sixth resistors. An emitter ofthe fourth bipolar transistor is grounded and the base thereof isconnected to the base bias current control terminal via the fifthresistor.

[0054] A collector of the fourth bipolar transistor is connected to thefirst resistor and the sixth resistor, and the sixth resistor isconnected to a power supply terminal.

[0055] It is assumed that a resistance of a circuit consisting the firstthrough third resistors and the second and third bipolar transistors,viewed from the base of the first bipolar transistor is defied as R, amutual conductance of the first bipolar transistor is defined as gm anda common-emitter current amplification factor is defines as h21.

[0056] Under such a circumstance, an emitter area of the first bipolartransistor and resistances of the first through third resistors areselected such that an impedance given by (1/gm+R/(h21+1)) is higher thanan impedance of the base of bipolar transistor for the power amplifierin a predetermined frequency band and is equivalent to an impedance ofthe base of the bipolar transistor for the power amplifier in a directcurrent.

[0057] The first through fourth bipolar transistors may be heterojunction bipolar transistors formed on an chemical substrate, and thefirst through fourth bipolar transistors may be Si homo BJTs formed on aSi substrate.

[0058] The first through fourth bipolar transistors may be SiGe heterojunction bipolar transistors formed on a Si substrate.

[0059] Further, the bipolar transistor for the power amplifier is formedon the same semiconductor substrate as the base bias circuit, and thebase bias circuit and the bipolar transistor for the power amplifier areconnected by a metal wiring formed by a semiconductor production processto constitute the power amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060]FIG. 1 shows an example of a power amplifier according to thisinvention;

[0061]FIG. 2 is a diagram for explaining a conventional base biascircuit;

[0062]FIG. 3 is a diagram for explaining an operation of a poweramplifier illustrated in FIG. 1;

[0063]FIG. 4 is a diagram for explaining an operation of a poweramplifier illustrated in FIG. 1;

[0064]FIG. 5 is the other example of a power amplifier according to thisinvention;

[0065]FIG. 6 is the other example of a power amplifier according to thisinvention;

[0066]FIG. 7 is the other example of a power amplifier according to thisinvention;

[0067]FIG. 8 is the other example of a power amplifier according to thisinvention;

[0068]FIG. 9 is the other example of a power amplifier according to thisinvention;

[0069]FIG. 10 is the other example of a power amplifier according tothis invention;

[0070]FIG. 11 is the other example of a power amplifier according tothis invention; and

[0071]FIG. 12 is the other example of a power amplifier according tothis invention.

BEST MODE EMBODYING THIS INVENTION

[0072] Hereinafter, this invention will be explained with reference tothe drawings.

[0073] At first, referring to FIG. 1, FIG. 3 and FIG. 4, a base biascircuit 1 is composed of npn type bipolar transistors 5, 7, 9 andresistors 4, 6, 14 integrated on the same semiconductor substrate.

[0074] An emitter of the transistor 5 is directly connected to a base ofthe power transistor 13 without an inductor for an RF choke andresistors. A matching circuit consisting of the base bias circuit 1, thepower transistor 13 and a passive device are fabricated on the samegallium arsenide substrate so as to totally constitute an MMICamplifier.

[0075] Further, each of the bipolar transistors 5, 7, 9 is GaAs/AlGaAshetero junction bipolar transistor (HBT) produced by the same process.

[0076] An area ratio of the bipolar transistors 5, 7, 9 is set to5:1:1:30, and an emitter dimension of the bipolar transistor 7, 9 havinga smallest emitter area is set to a smallest dimension permitted in theprocess. The total of the emitter areas of the transistors constitutingthe base bias circuit 1 is smaller than that of the conventionaltechnique.

[0077] Description will be made about an operation of an amplifiercircuit illustrated in FIG. 1.

[0078] A potential of a node 8 connected to the base of the bipolartransistor 7 is equal to the total of VBE of the bipolar transistor 9and VBE of the bipolar transistor 7. In the amplifier device, acollector current density of the bipolar transistor 9 is designed so asto be equal to a collector current density of the power transistor 13.

[0079] Therefore, VBE of the bipolar transistor 9 is equal to VBE of thepower transistor 13. Further, the collector current of the powertransistor 13 is higher with 30 times than the collector current of thebipolar transistor 9. Accordingly, the base current of the powertransistor 13 is higher with 30 times than the base current of thebipolar transistor 9.

[0080] The base current of the bipolar transistor 13 is equal to theemitter current of the bipolar transistor 5. The base current of thebipolar transistor 9 is equal to the emitter current of the bipolartransistor 7. In addition, the emitter area of the bipolar transistor 5is five times of that of the bipolar transistor 7, and therefore, thecollector current density of the bipolar transistor 5 becomes six timesof the collector current density of the bipolar transistor 7.

[0081] Therefore, VBE of the bipolar transistor 5 is higher than VBE ofthe bipolar transistor 7. Herein, the collector current of the bipolartransistor is generally proportional to exp (q×VBE/(k×T)), and takingthis into account, it is necessary that VBE of the bipolar transistor 5is higher with k×T×ln(6)/q than VBE of the bipolar transistor 7, andhigher with about 47 mV in the room temperature.

[0082] The resistance value of the resistor 6 and the resistor 14 isselected such that a voltage drop due to the resistor 6 in a standardoperation state is higher with 47 mV than the voltage drop due to theresistor 14.

[0083] Herein, explanation will be made of a current value and a circuitconstant of each portion in a typical operation state of the amplifiercircuit illustrated in FIG. 1.

[0084] The collector current when the RF input power is zero, namely,the collector bias current is 135 mA, and the collector current of thebipolar transistor 9 is 4.5 mA. The collector current density of thebipolar transistor 9 is equal to the collector bias current density ofthe power transistor 13. Since the emitter area of the bipolartransistor 9 is set to a smallest area permitted in the process, theconsumption current of the bias circuit is minimized.

[0085] The GaAs/AlGaAs hetero junction bipolar transistor for use in thesemiconductor device illustrated in FIG. 1 has hFE of approximately 30.Accordingly, the emitter current of the bipolar transistor 7 is 0.15 mA,and the base current of the bipolar transistor 7 is 0.005 mA. Further,the emitter current of the bipolar transistor 5 is 4.5 mA, and the basecurrent of the bipolar transistor 5 is 0.15 mA.

[0086] Therefore, the base current of the bipolar trasnsistor 7 and thebase current of the bipolar transistor 5 are sufficiently negligibly lowfor the collector current of the bipolar transistor 9. Moreover, thecurrent of 4.5 mA equal to the collector current of the bipolartransistor 9 flows along the resistor 4. The resistance value of theresistor 6 is 12Ω, and the voltage drop due to the resistor 6 becomes 54mV.

[0087] By contrast, the resistance value of the resistor 14 is 47Ω, andthe voltage drop due to the resistor 14 is 7 mV. The difference betweenthe voltage drop due to the resistor 6 and the voltage drop due to theresistor 14 becomes 47 mV. The resistance value of the resistor 4becomes 100Ω.

[0088] The collector current of the bipolar transistor 9 issubstantially equal to the current flowing along the resistors 4, 6.Herein, the potential of the node 8 is equal to 2.7 V as the total ofthe VBE of the bipolar transistor 9 and VBE of the bipolar transistor 7,and the fluctuation of such a voltage is small even if the collectorcurrent of the bipolar transistor 9 is fluctuated. Taking this intoconsideration, the collector current IC 9 of the bipolar transistor 9 isrepresented by IC=(Vref-2.7)/(100+12) by using the voltage V given tothe control terminal 2, so that IC 9=4.5 mA is obtained in the case ofVref=3.2V.

[0089] In this event, the collector bias current density of the bipolartransistor 13 is equal to that of the bipolar transistor 9 and thecollector bias current of the power transistor 13 becomes 135 mA.Herein, it is found out that the bias circuit is not affected by thepower supply voltage in such a structure because the power supplyvoltage does not appear in the equation for giving IC 9.

[0090] Moreover, when the environment temperature is fluctuated,characteristic of each bipolar transistor is also fluctuated. In thecircuit shown in FIG. 1, a portion consisting of the bipolar transistors7, 9 and a portion consisting of the bipolar transistor 5 and the powertransistor 13 are substantially symmetrical in the structure. Therefore,the affect of the characteristic fluctuation of the bipolar transistor 7and the affect of the characteristic fluctuation of the bipolartransistor 13 are cancelled while the affects of the characteristicfluctuations of the bipolar transistor 9 and the power transistor 5 arecancelled. As a consequence, the structure is not readily subjected tothe affect of the environment temperature. In the circuit shown in FIG.1, however, the symmetrical characteristic of the circuit is destroyedbecause the voltage drops due to the resistor 6 and the resistor 14 isutilized.

[0091] Therefore, the circuit is readily subjected to the affect of theenvironment temperature compared with the conventional circuitillustrated in FIG. 2. However, the voltage drops of the resistor 6 andthe resistor 14 are 54 mV and 7 mV, respectively, and are sufficientlylow in comparison with typical values (1.2-1.4 V) of VBE of theGaAs/AlGaAs hetero junction bipolar transistor.

[0092] Therefore, deterioration of resistance for the environmenttemperature fluctuation due to the insertion of the resistor 6 and theresistor 14 is sufficiently low.

[0093] Herein, when the resistance of the circuit consisting of theresistors 4, 6, 14 viewed from the base of the bipolar transistor 5 isdefined as R, the mutual conductance of the bipolar transistor 5 isdefined as gm, and the common-emitter current amplification factor isdefined as h21, the impedance of the base bias circuit 1 viewed the sideof the bipolar transistor 5 from the node 12 is given by(1/gm+R/(h21+1)). gm of the bipolar transistor is given by q×IC/(k×T)using the collector current IC. Since the collector current of thebipolar transistor 5 is 4.5 mA, 1/gm is equal to 5.8 Ω.

[0094] On the other hand, h21 is substantially equal to hFE under a lowfrequency, is varied with a ratio of −6 dB /oct. under a high frequency,and an absolute value of h21 is equal to 1 when the frequency is acutoff frequency fT. When the collector current of the bipolartransistor 5 is 4.5 mA, fT is about 5 GHz. Therefore, h21 is about 2.5in 2 GHz as the band of the amplifier.

[0095] The resistance value of the circuit consisting of the bipolartransistors 7, 9 viewed from the node 8 is twice of reciprocal of gm ofthe bipolar transistor 9. Herein, gm of the bipolar transistor is givenby q×IC/(k×T) and the collector current of the bipolar transistor 9 is4.5 mA. Taking this into consideration, the resistance value of thecircuit consisting of the bipolar transistors 7, 9 viewed from the node8 is equal to 11.6 Ω.

[0096] If it is assumed that the voltage source is connected to thecontrol terminal 2, the resistance R of the circuit consisting of theresistors 4, 6, 14 and the bipolar transistors 7, 9 viewed from the baseof the bipolar transistor 5 becomes 47+1/(1/100+1/(12+11.6))=6.1 Ω.

[0097] As mentioned above, the impedance viewed the side of the bipolartransistor 5 from the node 12 is given by (5.8+66.1/(h21+1)). Sinceh21=hFE=30 is given under the direct current, the impedance becomesh21=2.5 under 7.9 Ω, 2 GHz. Therefore, the impedance is equal to 24.7 Ω.

[0098] A schematic diagram of frequency characteristic of this impedanceis shown in FIG. 3.

[0099] In order to increase the impedance under the high frequency ofthe base bias circuit 1 viewed the side of the bipolar transistor 5 fromthe node 12, the resistance value of the resistor 15 must be increased.

[0100] By simultaneously optimizing the resistance value of the resistor6, the difference between the voltage drop due to the resistor 6 and thevoltage drop due to the resistor 14 can be kept to a desired value,namely, to 47 mV in this case.

[0101] In this event, attention is paid for the impedance of the base ofthe power transistor 13. Under the direct current, the impedance of thebase is represented by hFE/gm=hFE×k×T/(q×IC/)=30×0.026/0.135=5.8Ω. Thisvalue is equivalent to a value (7.9 Ω) of the impedance under the directcurrent viewed the side of the bipolar transistor 5 from the node 12 ofthe base bias circuit 1.

[0102] Therefore, the base bias circuit 1 operates like the voltagesource under the direct current. In the meantime, the impedance of thebase of the power transistor 13 under the high frequency is reduced toabout 1/3 of the value (5.8 Ω) under the direct current by the affect ofthe capacitor.

[0103] By contrast, the value of the impedance under 2 GHz viewed theside of the bipolar transistor 5 from the node 12 of the base biascircuit 1 is equal to 24.7 Ω, and is equal to ten times of the impedanceof the base of the power transistor 13 or higher.

[0104] Therefore, the leak to the base bias circuit 1 of the signalpower in the 2 GHz band given to the power transistor 13 can be lowerysuppressed without using the RF choke inductor between the powertransistor 13 and the bias circuit 1. The schematic diagram of thefrequency characteristic of this impedance is shown in FIG. 4.

[0105] In summary, the base bias circuit 1 illustrated in FIG. 1according to this invention can realize the facts required for the basecircuit for use in the power amplifier using the common-emitter bipolartransistor. Namely, the base bias circuit 1 operates like the constantvoltage source, the generated base bias voltage is not subjected to theaffect of the fluctuation of the power supply voltage, the generatedbias voltage is varied in dependence upon the environment temperaturefluctuation so as to keep the collector base current constant, and thebase bias voltage generated in accordance with the control signal fromthe external is variable.

[0106] Further, in the amplifier circuit using this invention, theresistor 6 and the resistor 14 are added, and the difference between thevoltage drop due to the resistor 6 and the voltage drop due to theresistor 14 is set to 47 mV, and thereby, the emitter area ratio of thebipolar transistors 7, 9 is set to 1:1 while the emitter area ratio ofthe bipolar transistor 5 and the power transistor 13 is set to 5:30, sothat the symmetrical characteristic of the circuit is destroyed in sucha structure.

[0107] As a consequence, the size of each bipolar transistorconstituting the bias circuit 1 is smaller than that of the amplifieraccording to the conventional technique, and the current consumed by thebias circuit 1 is reduced also. Moreover, by selecting the values of theresistors 6 and 14 to suitable values, namely, 12 Ω and 47 Ω in theamplifier illustrated in FIG. 1, the impedance of the base bias circuit1 under the high frequency viewed the side of the bipolar transistor 5from the node 12 can be sufficiently higher than the impedance of thebase of the power transistor 13.

[0108] Therefore, the leak to the base bias circuit 1 of the highfrequency signal power given to the power transistor 13 can be lowerysuppressed without inserting the RF choke inductor between the powertransistor 13 and the bias circuit 1.

[0109] Specifically, the cost reduction due to the reduction of theexterior parts as well as the reduction of the chip size due to thereduction of the on-chip inductors can be achieved.

[0110] Subsequently, referring to FIG. 5, a base bias circuit 15 iscomposed of an npn type GaAs/AlGAs hetero junction bipolar transistors19, 20, 21 and resistors 17, 18. Integrated on the same semiconductorsubstrate

[0111] An emitter of the transistor 21 is directly connected to the baseof the npn type GaAs/AlGaAs hetero junction bipolar transistor 22without an inductor and a resistor for the RF choke.

[0112] A matching circuit 23 consisting of the base bias circuit 15, thepower transistor 22 and a passive device is manufactured on the samegallium arsenide substrate to totally constitute an MMIC amplifier.

[0113] The emitter area ratio of the bipolar transistors 19, 20, 21, 22is set to 1:1:10:100, and the emitter dimension of the bipolartransistor 19, 20 having a smallest emitter area is set to a minimumdimension permitted in the process.

[0114] The total of the emitter areas of the transistors constitutingsuch a base bias circuit 15 is smaller than that in case using theconventional technique.

[0115] The base bias circuit 15 illustrated in FIG. 5 can realize thefacts required for the base circuit for use in the power amplifier usingthe common-emitter bipolar transistor. Namely, the base bias circuit 15operates like the constant voltage source, the generated base biasvoltage is not subjected to the affect of the fluctuation of the powersupply voltage, the generated bias voltage is varied in dependence uponthe environment temperature fluctuation so as to keep the collector basecurrent constant, and the base bias voltage generated in accordance withthe control signal from the external is variable.

[0116] Further, in the semiconductor device illustrated in FIG. 5, theresistor 18 is added, and the voltage drop due to the resistor 18 issuitably set and thereby, the emitter area ratio of the bipolartransistors 19, 20 is set to 1:1 while the emitter area ratio of thebipolar transistor 21 and the power transistor 22 is set to 10:100, sothat the symmetrical characteristic of the circuit is destroyed in sucha structure.

[0117] As a consequence, the size of each bipolar transistorconstituting the bias circuit 15 is smaller than that of thesemiconductor device according to the conventional technique, and thecurrent consumed by the bias circuit 15 is reduced also. In thesemiconductor device illustrated in FIG. 5, the resistance of theresistor 14 of the semiconductor device shown in FIG. 1 is equal tozeroΩ in such a structure.

[0118] However, the emitter area of each bipolar transistor and thevalues of the resistors 17, 18 are suitably balanced, and as a result,the impedance of the base bias circuit 15 under the high frequencyviewed the side of the bipolar transistor 21 from the node 24 issufficiently higher than the impedance of the base of the powertransistor 22, even if the resistor 14 is omitted.

[0119] Accordingly, the leak to the base bias circuit 1 of the highfrequency signal power given to the power transistor 22 can be lowerysuppressed without inserting the RF choke inductor between the powertransistor 22 and the bias circuit 15.

[0120] Specifically, the cost reduction due to the reduction of theexterior parts and the reduction of the chip size due to the reductionof the on-chip inductors can be achieved.

[0121] Referring to FIG. 6, a base bias circuit 25 is composed of an npntype Si homo bipolar transistor 30,31,32 and resistors 27, 28 integratedon the same semiconductor substrate

[0122] An emitter of the transistor 32 is directly connected to the baseof the npn type Si homo power transistor 33 without an inductor and aresistor for the RF choke.

[0123] The base bias circuit 25 and the power transistor 33 aremanufactured on the same Si substrate to constitute an MMIC externallyadded to a matching circuit.

[0124] A matching circuit 36 consisting of the passive devices ismanufactured on a dielectric substrate. In the semiconductor deviceshown in FIG. 6, the resistor 29 is added to the semiconductor deviceillustrated in FIG. 5. Since the resistor 28 and the resistor 29 areequivalent with respect to the circuit operation, the operation of thesemiconductor device shown in FIG. 6 is the same as that of thesemiconductor device shown in FIG. 5 in principle.

[0125] In other words, the base bias circuit 25 illustrated in FIG. 6can realize the facts required for the base circuit for use in the poweramplifier using the common-emitter bipolar transistor. Namely, the basebias circuit 25 operates like the constant voltage source, the generatedbase bias voltage is not subjected to the affect of the fluctuation ofthe power supply voltage, the generated bias voltage is varied independence upon the environment temperature fluctuation so as to keepthe collector base current constant, and the base bias voltage generatedin accordance with the control signal from the external is variable.

[0126] Further, in the semiconductor device illustrated in FIG. 6, theresistors 28, 29 are added, and the voltage drop due to the resistors28, 29 is suitably set and thereby, the symmetrical characteristicbetween the emitter area ratio of the bipolar transistors 30, 31 and theemitter area ratio of the bipolar transistor 32 and the power transistor33 is destroyed in such a structure.

[0127] As a consequence, the size of each bipolar transistorconstituting the bias circuit 25 is smaller than that of thesemiconductor device according to the conventional technique, and thecurrent consumed by the bias circuit 25 is reduced also. Further, theimpedance of the base bias circuit 25 under the high frequency viewedthe side of the bipolar transistor 32 from the node 34 is sufficientlyhigher than the impedance of the base of the power transistor 33.

[0128] Therefore, the leak to the base bias circuit 25 of the highfrequency signal power given to the power transistor 33 can be lowerysuppressed without inserting the RF choke inductor between the powertransistor 33 and the bias circuit 25.

[0129] Specifically, the cost reduction due to the reduction of theexterior parts and the reduction of the chip size due to the reductionof the on-chip inductors can be achieved.

[0130] Referring to FIG. 7, a base bias circuit 37 is composed of an npntype SiGe base bipolar transistor 39,40,41 and resistors 43, 44integrated on the same semiconductor substrate.

[0131] An emitter of the transistor 41 is directly connected to the baseof the npn type SiGe base power transistor 42 without an inductor forand a resistor for the RF choke.

[0132] The base bias circuit 37 and the power transistor 42 aremanufactured on the same Si substrate to constitute an MMIC externallyadded to a matching circuit. A matching circuit 46 consisting of passivedevices is manufactured on a dielectric substrate.

[0133] In the semiconductor device shown in FIG. 7, the resistor 28 ofthe semiconductor device illustrated in FIG. 5 is omitted. Since theresistor 28 and the resistor 29 are equivalent with respect to thecircuit operation, the operation of the semiconductor device shown inFIG. 7 is the same as that of the semiconductor device shown in FIG. 6in principle.

[0134] In other words, the base bias circuit 37 illustrated in FIG. 7can realize the facts required for the base circuit for use in the poweramplifier using the common-emitter bipolar transistor. Namely, the basebias circuit 25 operates like the constant voltage source, the generatedbase bias voltage is not subjected to the affect of the fluctuation ofthe power supply voltage, the generated bias voltage is varied independence upon the environment temperature fluctuation so as to keepthe collector base current constant, and the base bias voltage generatedin accordance with the control signal from the external is variable.

[0135] Further, in the semiconductor device illustrated in FIG. 7, theresistor 44 is added, and the voltage drop due to the resistor 44 issuitably set and thereby, the symmetrical characteristic between theemitter area ratio of the bipolar transistors 39, 40 and the emitterarea ratio of the bipolar transistor 41 and the power transistor 42 isdestroyed in such a structure.

[0136] As a consequence, the size of each bipolar transistorconstituting the bias circuit 37 is smaller than that of thesemiconductor device according to the conventional technique, and thecurrent consumed by the bias circuit 37 is reduced also. Further, theimpedance of the base bias circuit 37 under the high frequency viewedthe side of the bipolar transistor 41 from the node 45 is sufficientlyhigher than the impedance of the base of the power transistor 42.

[0137] Therefore, the leak to the base bias circuit 37 of the highfrequency signal power given to the power transistor 42 can be lowerysuppressed without inserting the RF choke inductor between the powertransistor 42 and the bias circuit 37.

[0138] Specifically, the cost reduction due to the reduction of theexterior parts and the reduction of the chip size due to the reductionof the on-chip inductors can be achieved.

[0139] Referring to FIG. 8, a base bias circuit 48 is composed ofn-channel MOSFETs 50, 51, an npn type Si homo bipolar transistor 63 andresistors 65, 66 integrated on the same semiconductor substrate. Asource of the MOSFET 51 is directly connected to the base of the npntype Si homo power transistor 64 without an inductor and a resistor fora RF choke.

[0140] The base bias circuit 48 and the power transistor 64 aremanufactured on the same Si substrate to constitute an MMIC externallyadded to a matching circuit. A matching circuit 68 consisting of thepassive devices is manufactured on a dielectric substrate.

[0141] In the semiconductor device shown in FIG. 8, the bipolartransistors 5, 7 of the semiconductor device shown in FIG. 5 arereplaced with the MOSFETs 50, 51. In the semiconductor deviceillustrated in FIG. 8, the circuit portion consisting of the MOSFET 50and the bipolar transistor 63 and the circuit portion consisting of theMOSFET 51 and the bipolar transistor 64 has the symmetrical structure,and therefore, the operation of the semiconductor device shown in FIG. 8is the same as that of the semiconductor device shown in FIG. 5 inprinciple.

[0142] In other words, the base bias circuit 48 illustrated in FIG. 8can realize the facts required for the base circuit for use in the poweramplifier using the common-emitter bipolar transistor. Namely, the basebias circuit 48 operates like the constant voltage source, the generatedbase bias voltage is not subjected to the affect of the fluctuation ofthe power supply voltage, the generated bias voltage is varied independence upon the environment temperature fluctuation so as to keepthe collector base current constant, and the base bias voltage generatedin accordance with the control signal from the external is variable.

[0143] Further, in the semiconductor device illustrated in FIG. 8, theresistors 65, 66 are added, and the voltage drop due to the resistors65, 66 is suitably set and thereby, the symmetrical characteristicbetween the ratio of the gate width of the MOSFET 50 and the emitterarea ratio of the bipolar transistor 63 and the ratio of the gate widthof the MOSFET 51 and the emitter area ratio of the bipolar transistor 64is destroyed in such a structure.

[0144] As a consequence, the size of each bipolar transistorconstituting the bias circuit 48 is smaller than that of thesemiconductor device according to the conventional technique, and thecurrent consumed by the bias circuit 48 is reduced also. Further, theimpedance of the base bias circuit 48 under the high frequency viewedthe side of the MOSFET 51 from the node 67 is sufficiently higher thanthe impedance of the base of the power transistor 64.

[0145] Therefore, the leak to the base bias circuit 48 of the highfrequency signal power given to the power transistor 64 can be lowerysuppressed without inserting the RF choke inductor between the powertransistor 64 and the bias circuit 48.

[0146] Specifically, the cost reduction due to the reduction of theexterior parts added and the reduction of the chip size due to thereduction of the on-chip inductors can be achieved.

[0147] Referring to FIG. 9, in a base circuit 70, a buffer circuit 72 isnewly added to the control terminal 2 of the base bias circuit 15 shownin FIG. 5. Basic operation, function and effect of the semiconductordevice illustrated in FIG. 9 are the same as those of the semiconductordevice shown in FIG. 5.

[0148] By adding the buffer circuit 72, the current flowing to thecontrol terminal 71 becomes low, so that the bias circuit 70 can besufficiently driven by the use of the control signal generated by an LSImanufactured through the typical CMOS process.

[0149] Referring to FIG. 10, in a base circuit 76, a buffer circuit 77is newly added to the control terminal 2 of the base bias circuit 15shown in FIG. 5. Basic operation, function and effect of thesemiconductor device illustrated in FIG. 10 are the same as those of thesemiconductor device shown in FIG. 5.

[0150] The buffer circuit 77 serves as an inverting amplifier consistingof the resistors 78, 79 and the bipolar transistor 80. By adding thebuffer circuit 77, the current flowing to the control terminal 71becomes low, so that the bias circuit 76 can be sufficiently driven bythe use of the control signal generated by an LSI manufactured throughthe typical CMOS process.

[0151] Since the buffer circuit 77 is the inverting amplifier, therelationship between the control voltage and the collector bias currentof the power transistor 80 is inverted in the base bias circuit 76 incomparison with the base bias circuit 15 shown in FIG. 5.

[0152] Referring to FIG. 11, a base bias circuit 86, a power transistor87, a matching circuit 88, and an MIN capacitor 91 for cutting DC areintegrated in the same GaAs substrate 85. As the transistors, npn typeGaAs/AlGaAs hetero junction bipolar transistors are totally used. Thematching circuit 88 is composed of a spiral inductor 89 and an MINcapacitor 90.

[0153] Basic operation, function and effect of the semiconductor deviceillustrated in FIG. 11 are the same as those of the semiconductor deviceshown in FIG. 5.

[0154] Referring to FIG. 12, base bias circuits 94, 95, powertransistors 99, 102, MIN capacitors 98, 100, 104, and a resistor 103 areintegrated on the same Si substrate 93. As the transistors, npn type Sihomo junction bipolar transistor are totally used.

[0155] The semiconductor device constitutes the MMIC using two stagesamplifiers, and the impedance viewed from the RF input terminal 97 inthe band of the amplifier is matched to 50 Ω by the operation of a feedback circuit consisting of the resistor 103 and the MIN capacitor 104.The matching between the stages is adjusted by an external circuit addedto the connection terminal 96 to the external circuit. The outputmatching is adjusted by the external circuit connected to the RF outputterminal 101. The base bias circuit 95 has the same basic structure asthe base bias circuit 94, and the respective circuit constants areoptimized in accordance with the difference of the emitter areas of thepower transistors 99 and 102. Basic operation, function and effect ofthe base bias circuits 94 and 95 are the same as those of the base biascircuit 15 shown in FIG. 5.

Industrial Applicability

[0156] According to this invention, the chip area and the consumptioncurrent can be reduced, and the choke inductor between the base of thepower transistor and the bias supply circuit is unnecessary.

1. A base bias circuit which supplies a bias current to a base of acommon-emitter bipolar transistor of an npn type for a power amplifier,wherein: the base bias circuit comprises first through third bipolartransistors of an npn type and first and second resistors integrated ona semiconductor substrate and a base bias current control terminal, thefirst resistor is inserted between the base bias current controlterminal and the first bipolar transistor, the second resistor isinserted between a base of the second bipolar transistor and the firstbipolar transistor, a base of the second bipolar transistor is connectedto a collector of the third bipolar transistor, an emitter of the secondbipolar transistor is connected to a base of the third bipolartransistor, an emitter of the third bipolar transistor is grounded, acollector of the first bipolar transistor is connected to a positivepower supply, and an emitter of the first bipolar transistor is directlyconnected to the base of the bipolar transistor for the power amplifier.2. A base bias circuit as claimed in claim 1, wherein: a third resistoris inserted between a connection point of the first and second resistorand a base of the first bipolar transistor.
 3. A base bias circuit asclaimed in claim 1, wherein: the emitter of the third bipolar transistoris grounded via a fourth resistor.
 4. A base bias circuit as claimed inclaim 1, wherein: the emitter of the third bipolar transistor isgrounded via the fourth resistor, and is short-circuited by the use of ametal wiring instead of the second resistor.
 5. A base bias circuit asclaimed in claim 1, wherein: the first and second bipolar transistorsare replaced by n-type MOSFETs.
 6. A base bias circuit as claimed inclaim 1, wherein: a buffer circuit is inserted between the firstresistor and the base bias current control terminal.
 7. A base biascircuit as claimed in claim 6, wherein: the buffer circuit comprises afourth bipolar transistor of an npn type and fifth and sixth resistors,an emitter of the fourth bipolar transistor is grounded and the basethereof is connected to the base bias current control terminal via thefifth resistor, a collector of the fourth bipolar transistor isconnected to the first resistor and the sixth resistor, and the sixthresistor is connected to a power supply terminal.
 8. A base bias circuitas claimed in claim 2, wherein: when a resistance of a circuitconsisting the first through third resistors and the second and thirdbipolar transistors, viewed from the base of the first bipolartransistor is defied as R, a mutual conductance of the first bipolartransistor is defined as gm and a common-emitter current amplificationfactor is defines as h21, an emitter area of the first bipolartransistor and resistances of the first through third resistors areselected such that an impedance given by (1/gm+R/(h21+1)) is higher thanan impedance of the base of bipolar transistor for the power amplifierin a predetermined frequency band and is equivalent to an impedance ofthe base of the bipolar transistor for the power amplifier in a directcurrent.
 9. A power amplifier, wherein: the bipolar transistor for thepower amplifier is formed on the same semiconductor substrate as thebase bias circuit as claimed in claim 1, and the base bias circuit andthe bipolar transistor for the power amplifier are connected by a metalwiring formed by a semiconductor production process.
 10. A base biascircuit as claimed in claim 1, wherein: the first through third bipolartransistors are hetero junction bipolar transistors formed on a chemicalsubstrate.
 11. A base bias circuit as claimed in claim 7, wherein: theforth bipolar transistor is a hetero junction bipolar transistor formedon a chemical substrate.
 12. A base bias circuit as claimed in claim 1,wherein: the first through third bipolar transistors are Si homo BJTsformed on a Si substrate.
 13. A base bias circuit as claimed in claim 7,wherein: the fourth bipolar transistor is a Si homo BJT formed on a Sisubstrate.
 14. A base bias circuit as claimed in claim 1, wherein: thefirst through third bipolar transistors are SiGe hetero junction bipolartransistors formed on a Si substrate.
 15. A base bias circuit as claimedin claim 7, wherein: the fourth bipolar transistor is a SiGe heterojunction bipolar transistor formed on a Si substrate.